Add SMTP healthcheck

Signed-off-by: Knut Ahlers <knut@ahlers.me>

pkg/healthcheck/registry.go

@@ -6,6 +6,7 @@ import (
 	"git.luzifer.io/luzifer/ipt-loadbalancer/pkg/config"
 	"git.luzifer.io/luzifer/ipt-loadbalancer/pkg/healthcheck/common"
 	"git.luzifer.io/luzifer/ipt-loadbalancer/pkg/healthcheck/http"
+	"git.luzifer.io/luzifer/ipt-loadbalancer/pkg/healthcheck/smtp"
 	"git.luzifer.io/luzifer/ipt-loadbalancer/pkg/healthcheck/tcp"
 	"github.com/Luzifer/go_helpers/v2/fieldcollection"
 )
@@ -25,6 +26,9 @@ func ByName(name string) Checker {
 	case "http":
 		return http.New()
 
+	case "smtp":
+		return smtp.New()
+
 	case "tcp":
 		return tcp.New()
 

pkg/healthcheck/smtp/smtp.go

@@ -0,0 +1,88 @@
+// Package smtp contains a health-check to verify a SMTP server is
+// indeed listening to SMTP protocol
+package smtp
+
+import (
+	"crypto/tls"
+	"fmt"
+	"net"
+	"net/smtp"
+	"time"
+
+	"git.luzifer.io/luzifer/ipt-loadbalancer/pkg/config"
+	"git.luzifer.io/luzifer/ipt-loadbalancer/pkg/healthcheck/common"
+	"github.com/Luzifer/go_helpers/v2/fieldcollection"
+)
+
+const (
+	settingInsecureTLS = "insecureTLS"
+	settingPort        = "port"
+	settingTimeout     = "timeout"
+	settingTLS         = "tls"
+)
+
+type (
+	// Check represents the SMTP check
+	Check struct{}
+)
+
+var (
+	defInsecureTLS = false
+	defTimeout     = time.Second
+	defTLS         = false
+)
+
+// New returns a new SMTP check
+func New() Check { return Check{} }
+
+// Check executes the check
+func (c Check) Check(settings *fieldcollection.FieldCollection, target config.Target) error {
+	conn, err := net.DialTimeout(
+		"tcp",
+		fmt.Sprintf("%s:%d", target.Addr, settings.MustInt64(settingPort, c.intToInt64Ptr(target.Port))),
+		settings.MustDuration(settingTimeout, &defTimeout),
+	)
+	if err != nil {
+		return fmt.Errorf("dialing tcp: %w", err)
+	}
+
+	sc, err := smtp.NewClient(conn, "localhost")
+	if err != nil {
+		return fmt.Errorf("creating SMTP client: %w", err)
+	}
+
+	if settings.MustBool(settingTLS, &defTLS) {
+		tc := &tls.Config{
+			InsecureSkipVerify: settings.MustBool(settingInsecureTLS, &defInsecureTLS), //nolint:gosec // That's intended
+		}
+
+		if err = sc.StartTLS(tc); err != nil {
+			return fmt.Errorf("starting TLS: %w", err)
+		}
+	}
+
+	if err = sc.Hello("localhost"); err != nil {
+		return fmt.Errorf("exchanging HELO: %w", err)
+	}
+
+	if err = sc.Close(); err != nil {
+		return fmt.Errorf("closing connection: %w", err)
+	}
+
+	return nil
+}
+
+// Help returns the set of settings used in the check
+func (Check) Help() (help []common.SettingHelp) {
+	return []common.SettingHelp{
+		{Name: settingInsecureTLS, Default: defInsecureTLS, Description: "Skip TLS certificate validation"},
+		{Name: settingPort, Default: "target-port", Description: "Port to send the request to"},
+		{Name: settingTimeout, Default: defTimeout, Description: "Timeout for the HTTP request"},
+		{Name: settingTLS, Default: defTLS, Description: "Connect to port using TLS"},
+	}
+}
+
+func (Check) intToInt64Ptr(i int) *int64 {
+	i64 := int64(i)
+	return &i64
+}